okay to insulate existing walls w/o vapor barrier?


Old 07-09-01, 12:04 PM
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I'm interested in having my exterior walls insulated. My house was built in 1930. Currently, the walls are vinyl, tyvek, cedar shingles, sheathing, empty space, lath and plaster. The house is considered to be "1.5" stories- with the middle portion of the top floor being rooms and the sides attic.

Here are my questions:

Is tyvek considered to be a "vapor barrier"? From what I've read on previous threads, it doesn't appear to be. If that's the case, is it safe to insulate my walls? Could the insulation trap moisture and then give me rot problems? Also, I've read where the vapor barier should be on the inside. Will this be a problem?

Except where there are windows, it is currently possible to get to 2 of the outer walls from my attic- I can see all the way from the attic to the sill of the foundation. Can insulation be blown from up there? I don't really care to fix too many holes in the plaster or vinyl siding...

What types of insullation are being used when it's blown in/filled for existing walls these days? Are they able to use that newer foam stuff?

My house is about 1400 sq. feet. What would a range figure be for insulating the walls and portions of the attic? I realize it's tricky without seeing it, but might it be $5K, $10K, $15? I have no idea how much...

Thanks much! Even though I don't really want to "do it myself", this is the only insulation forum I can find on the 'net. I noticed with ~1300 threads, it is one of the busier forums on this site!
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Old 07-09-01, 11:53 PM
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Tyvek is indeed a vapor barrier. I have a raincoat made from the stuff. If you use a quality cellulose insulation, moisture won't be a problem. The insulation will have enough aluminum chlorhydrate (the stuff they put in underarm deodorant) in it to evaporate any moisture that may come in contact with it. Whether you need a vapor barrier on the inside (under the lathe and plaster) of the wall or not depends on the climate you live in.

If you remove the top 2 courses of the vinyl siding and blow the insulation in from the outside, there won't be any holes to plug. Chances of being able to blow the walls from the attic are pretty slim. Generally not enough work space there to do it.

Blowing walls with cellulose is not all that difficult, IF you have the right equipment. The problems that arise are generally the result of the contractor using a machine with too much volume for doing walls and trying to get the job done in a hurry. Walls take time! The foam you are referring to would require that either the inside or the outside of every wall be totally removed to blow it. Probably not what you have in mind.

A 1400 sq. ft. home should cost about $2,000 tops to blow cellulose into the walls. Could be more if you live in S.F., L.A., NYC, etc. Best way to find out is to get quotes.
Old 07-10-01, 12:54 PM
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Lefty- thanks a bunch for your reply. Very helpful!

ps- left handers rule!
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